The present invention relates to a braking pressure modulator of the type comprising a volume-receiving unit which is designed as a displacement-type or plunger system, whose displacement or plunger working chamber is interposed or adpated to be interposed between a master brake cylinder or the like and a wheel brake cylinder or the like of a brake system and which is further adapted to be uncoupled from the master brake cylinder or the like by a separating valve which closes automatically when the displacement member or plunger has been shifted in the working chamber for the purpose of modulating the pressure in the working chamber and wheel brake cylinder or the like. The system to which the invention relates further includes an actuator having an adjusting member that is coupled to the displacement member or plunger by way of a gear unit that is transmission responsive to the regulating distance. The adjusting member is engaged for being driven with a piston and diaphragm assembly. The adjusting member will generate an adjusting force that is dependent on the difference in pressure across the piston and diaphragm.
Braking pressure modulators are an essential component part of brake systems with anti-lock apparatus. As soon as slip sensors assigned to the vehicle wheels detect a locking wheel during braking of the vehicle, the braking pressure modulator associated with that wheel will be actuated. That is, the displacement member or plunger of the volume-receiving unit connected upstream from the wheel brake cylinder of the locking wheel will be adjusted in a direction for shifting the displacement member or plunger out of the working chamber while the separating valve automatically isolates the working chamber and thus also isolates the respective wheel brake cylinder from the master brake cylinder. The pressure in the working chamber as well as in the wheel brake cylinder will decrease more or less exponentially in dependence on the stroke of the displacement member or plunger. As a result, the brake force acting upon the locking wheel will be correspondingly reduced and the wheel will begin to rotate again when the brake force is reduced sufficiently. Subsequently, the displacement member or plunger is again shifted into the working chamber of the volume-receiving unit until the wheel starts to lock again and the separating valve opens again when the plunger or displacement member has reassumed its in or end position in the working chamber. The action described above will be successively repeated as needed.
The power consumption in conventional braking pressure modulators is relatively great. This is not desirable in principle because normally this power must be generated by the vehicle engine and thus is not at disposal for the vehicle's movement. Moreover, it has to be taken into account that the adjusting forces necessary for adjusting the displacement member or plunger of the volume-receiving unit are usually produced by utilizing the vacuum of the internal-combustion engine driving the vehicle. It can be expected from future engine developments, however, that utilizable engine vacuum will be reduced.